Method for identifying a transfer unit which is part of a connection between a communications terminal and a private branch exchange

ABSTRACT

Communication terminals are connected to a communication network via at least one hub having an unambiguous address in the communication network. Data transmission between the switching system and the communication terminals is provided using a time-slot-oriented data format formed from a periodic sequence of channel-oriented information segments. The address of the hub is transmitted from the hub to the switching system in an agreed information segment.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention pertains to data transmission systems generally,and in particular to transmission systems for time-slot-oriented data.

2. Discussion of the Related Art

A transmission system for transmitting time-slot-oriented data betweenan exchange termination and a line termination is usually part of acommunication system having a switching facility and subscriber linefacilities. The subscriber line facilities have subscriber interfacesfor connecting communication terminals to the communication system.

According to the ITU-T G.960 Standard, the subscriber line facilitiesare connected to the switching facility of the communication system viaa line termination and an exchange termination. Such a communicationsystem is used for setting up and, respectively, clearing downnarrow-band communication connections between communication terminalsconnected to the subscriber line facilities and to provide fornarrow-band communication—for example voice or datacommunication—between the communication terminals.

In modern communication systems, data transmission between the exchangetermination and the line termination usually takes place on the basis ofthe time-slot-oriented data format IOM-2 (ISDN Oriented ModularInterface) formed from a periodic sequence of channel-individualinformation segments—called time-division multiplex channel in the textwhich follows. As a rule, one time-division multiplex channel is in eachcase allocated to each subscriber interface of a subscriber linefacility in this arrangement.

In modern communication engineering, there is a need for broadbandtransmission of information such as, for example, still and movingpictures in videophone applications or of large volumes of data in theInternet. This increases the significance of transmission techniques forhigh and variable data transmission rates (greater than 100 Mbit/s)which take into account both the requirements of the data transmission(high speed at variable transmission bit rate) and the requirements ofvoice data transmission (maintaining time correlations with a datatransmission via a network) so that the separate networks currentlyexisting for the various purposes can be integrated in one network. Aknown data transmission method for high data speeds is the so-calledAsynchronous Transfer Mode (ATM). Data transmission on the basis of theAsynchronous Transfer Mode currently enables a variable transmission bitrate of up to 622 Mbit/s to be obtained.

In the cell-based data transmission method known as AsynchronousTransfer Mode (ATM), so-called ATM cells are used for transportingfixed-length data packets. An ATM cell is composed of a so-called“header” with a length of five bytes which contains switching datarelevant to the transportation of an ATM cell, and a so-called “payload”with a length of 48 bytes.

Data transmission via an ATM-based network generally takes place inso-called virtual paths or virtual channels. For this purpose,interconnection tables with switching information consisting of avirtual channel identifier and of a virtual path identifier are set upin the respective ATM network nodes of the ATM-based network by anexchange of signaling information during a connection set-up before thebeginning of the actual user data transmission. In the interconnectiontables, a so-called VCI value is assigned to the virtual channelidentifier and a so-called VPI value is assigned to the virtual pathidentifier.

The switching information entered in the interconnection table of an ATMnetwork node establishes how the virtual paths or, respectively, virtualchannels contained in the virtual paths of the incoming and outgoingconnections at the ATM network node are correlated with one another bythe signaling, that is to say which input is connected to which outputby a switching. ATM cells transmitted via these virtual connections(virtual paths and virtual channels) have switching data essentiallyconsisting of a VPI value and a VCI value in the header. The ATM headerdata are processed, i.e. the switching data arranged therein aredetected and evaluated at the input of an ATM network node. The ATMcells are then switched through by the ATM network node to an output ofthe ATM network node representing a certain destination by means of theswitching information stored in the interconnection table.

German Offenlegungsschrift DE 196 04 244 A1, shows a transmission systembetween an exchange termination and a line termination in whichtransmission is implemented via an ATM-based network. In thisarrangement, subscriber interfaces for connecting ISDN (IntegratedServices Digital Network) oriented communication terminals by ATM hubsconnected to the ATM-based network are provided. The exchangetermination of the communication system and the line terminationimplemented by the ATM hub have an ATM interface unit via which, on theone hand, a connection to the ATM-based network is implemented and, onthe other hand, the IOM-2 data format usually provided for a datatransmission between the exchange termination and the line terminationis converted to the ATM-based data format. Or, the ATM-based data formatis converted to the IOM-2 data format.

For addressing a subscriber interface of the ATM hub via the ATM-basednetwork, a permanently set up ATM channel of the ATM-based network isallocated to each time-division multiplex channel of the IOM-2 dataformat, i.e. an unambiguous VPI/VCI address is allocated to eachsubscriber interface of an ATM hub for a data transmission via theATM-based network. The VPI-VCI addresses are allocated to the respectivesubscriber interfaces and managed manually in the switching system.

If a fault occurs at a subscriber interface or at a communicationterminal connected to the subscriber interface, only the VPI/VCI addressof the defective subscriber interface or of the communication terminalconnected to the subscriber interface is known in the switching system.It is not possible to find the ATM hub associated with the communicationterminal.

A method for finding the association of a communication terminal with asubscriber interface of an ATM hub which is already used is the tracingback of the path in the ATM-based network starting from the switchingsystem to the communication terminal, i.e. determining the path in theATM-based network by means of the switching information stored in theATM network nodes. In most cases, however, this is not possible sincethe operator of the ATM-based network is not, as a rule, the operator ofthe telecommunication network implemented on this. The switchinginformation stored in the ATM network nodes is thus not available to theoperator of the telecommunication network.

Thus, according to the terminology of the ITU-T G.960 Standard (3/93)“access digital section for ISDN basic rate access”, especially pages 2and 3, the present invention is based on data transmission occurring atthe V reference point.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a method fordetermining the ATM hub associated with a communication terminal in asimple manner.

It is another object of the invention to provide a method that caneasily be implemented without making changes at the interface betweenswitching system and ATM hub.

It is an additional object of the invention to provide a method whereinthe susceptibility to faults is reduced by an automatic detection of theassociation between a communication terminal and an ATM hub.

It is a further object of the invention to provide a method whereinexisting free transmission capacities are utilized by way of a monitorchannel for transmitting the address of an ATM hub to a switchingsystem.

These and other objects of the invention will become apparent from areview of the following detailed description of the preferredembodiment, which is to be read in conjunction with a review of theaccompanying drawing figures.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a diagrammatic representation of an IOM-2 data format;

FIG. 2 shows a diagrammatic representation of essential functional unitsaccording to the present invention;

FIG. 3 shows a diagrammatic representation of a conversion of atime-slot-oriented data format into an ATM data format according to thepresent invention; and

FIG. 4 shows a diagrammatic representation of a conversion of anothertime-slot-oriented data format into an ATM data format according to thepresent invention.

DETAILED DESCRIPTION OF THE REFERRED EMBODIMENTS

To obtain a better understanding of the operation of a transmission oftime-slot-oriented data between an exchange termination and a linetermination, here is a discussion of basic principles.

Time-slot-oriented data are usually transmitted between an exchangetermination and a line termination on the basis of a known data format.An example of which is IOM-2 described in the product document “ICs forCommunications—IOM®-2 Interface Reference Guide” by Siemens, Munich,3/91, order No. B115-H6397-X-X-7600, particularly pages 6 to 12.

FIG. 1 shows a diagrammatic representation of the IOM-2 data formatwherein time division multiplex frames IOM-R having a length of 125 μsare periodically transmitted. Such a time-division multiplex frame IOM-Ris divided into time-division multiplex channels or subframes CH0–CH7,which are frequently simply called ‘channels’ in the literature.

The subframes CH0–CH7, in turn, are subdivided into two 8-bit-longpayload channels B1, B2, into an 8-bit-long monitor channel M, into a2-bit-long control information channel DI, into a 4-bit-long statuschannels C/I (Command/Indicate), and into two monitor status channelsMR, MX which in each case have a length of 1 bit. The controlinformation channel DI, the status channel C/I and the two monitorstatus channels MR, MX are usually combined and referred to as a controlinformation channel D. Channel D is sometimes referred to as signalingchannel D.

Via the user data channels B1, B2, user data are transmitted betweenfacilities connected to an IOM-2 bus with a transmission bit rate of 64kbit/s in each case. Via the control information channel D, controlinformation associated with the user data are transmitted at atransmission bit rate of 16 kbit/s. The monitor channel is used, amongother things, for configuring facilities connected to an IOM-2 bus onthe basis of a so-called ‘IOM-2 bus master’. Via the monitor statuschannels MR (Monitor Read) and MX (Monitor Transmit) it is establishedwhether data from a facility connected to the IOM-2 bus are read fromthe IOM-2 bus (MR=1, MX=0) or are output to the IOM-2 bus (MR=0, MX=1).Via the status channel C/I, information on real-time requirementsexisting for a data transmission between two facilities connected to theIOM-2 bus are exchanged.

FIG. 2 shows a diagrammatic representation of a PBX (Private BranchExchange) switching system with an exchange termination (ET) arrangedtherein. The exchange termination ET is connected to an ATM-basedcommunication network ATM-KN via an interface unit AE.

Furthermore, ATM hubs ATM-HUB, which have subscriber interfaces forconnecting communication terminals to the ATM-based communicationnetwork ATM-KN, are connected to the ATM-based communication networkATM-KN. Communication terminals are shown by way of example.

ISDN (Integrated Services Digital Network) communication terminals areusually connected to the ATM-based communication network ATM-KN by meansof S₀ interfaces. Or, digital communication terminals are usuallyconnected to the ATM-based communication network ATM-KN by means ofinterfaces derived therefrom, such as for example, U_(p0) interfaces,via an ATM hub. In general, a U_(p0) or an S₀ interface comprises, onthe one hand, two user data channels which are equipped with atransmission rate of 64 kbit/s in each case as ISDN-oriented B channels,and on the other hand, a signaling channel configured as anISDN-oriented D channel with a transmission rate of 16 kbit/s.Furthermore, it is generally possible to connect analog communicationterminals to the ATM-based communication network ATM-KN via a/binterfaces.

Communication terminals are connected to the ATM hub ATM-HUB. Thus, thesubscriber interfaces are provided by the ATM hub ATM-HUB by networkterminations NT according to the terminology of the ITU-T G.960Standard. Based upon the ITU-T G.960 Standard, the network terminationsof an ATM hub ATM-HUB are connected to the exchange termination ET ofthe switching system PBX via a line termination LT arranged in the ATMhub ATM-HUB. For a data transmission via the ATM-based communicationnetwork ATM-KN, the line termination LT, corresponding to the exchangetermination ET of the switching system PBX, is connected to theATM-based communication network ATM-KN via an interface unit AE.

Interface units AE provide a bi-directional conversion between thetime-slot-oriented IOM-2 data format usually provided for a datatransmission between the exchange termination and the line termination,and the packet-oriented ATM data format according to two differentconversion modes, which will be explained in greater detail below.

FIG. 3 shows a diagrammatic representation of the conversion of theIOM-2 data format into the ATM data format according to the firstconversion mode. In this mode, time-slot-oriented data are packed byteby byte into ATM cells according to the first ATM adaptation layer AAL1on the basis of the CES 2.0 rule of the ATM Forum. The ATM adaptationlayer AAL is used for adopting the ATM cell format to the network layer(Layer 3) of the OSI (Open System Interconnection) Reference Model.

In a conversion of the time-slot-oriented data format to thepacket-oriented ATM data format, each subframe CHx is allocated anunambiguous VPI/VCI address for transmission via the ATM-basedcommunication network ATM-KN. Thus, data allocated to differentsubframes CHx, are transmitted in separate ATM cells ATMZ having anunambiguous VPI/VCI address stored in the header H of the ATM cell ATMZ,which is shown by way of example with the VPI/VCI address VPI/VCIx forsubframe CH0 and with VPI/VCI address VPI/VCIy for subframe CH1.

In addition to the header H of the ATM cell ATMZ, the first byte in thepayload area is defined as pointer Z. This pointer Z points to the firstbyte of the data allocated to a subframe CHx within the payload area ofan ATM cell ATMZ. This pointer Z provides the possibility of restoringsynchronization between transmitter and receiver in the case where oneor more ATM cells ATMZ have been lost, such as due to a transmissionfault.

The first ATM adaptation layer AAL1, in a byte-by-byte manner, convertsall 4 channels following one another in time in a subframe CHx, to theATM cell format according to the ECMA Standard 277 (StandardizingInformation and Communication Systems), including the two payloadchannels B1, B2, the monitor channel M and the control channel D.

Payload information is transmitted beginning with the second byte of thepayload area of an ATM cell ATMZ. The data allocated to the individualchannels of a subframe CHx, shown by way of example for subframes CH0,CH1 in the figure, are transmitted in succession beginning with the dataof the control channel D, followed by the data of the monitor channel M,the data of the first payload channel B1 and the data of the secondpayload channel B2.

Following insertion of the data of the second payload channel B2 intothe payload area of an ATM cell ATMZ, the data of the control channel Dof the corresponding following subframe CHx, shown by way of example forsubframes CH0, CH1 in the figure, are read in.

Bytes arranged in the payload area of an ATM cell ATMZ are thusallocated to a channel, to the first payload channel B1, to the secondpayload channel B2, to the monitor channel M and to the control channelD, of a subframe CHx via the position of the byte in the payload area ofthe ATM cell ATMZ.

FIG. 4 shows the conversion of the IOM-2 data format into the ATM dataformat according to the second conversion mode in a diagrammaticrepresentation. In this mode time-slot-oriented data are packed byte bybyte into ATM cells ATMZ according to the second ATM adaptation layerAAL2. In the second ATM adaptation layer AAL2, it is possible tosubdivide the payload area of an ATM cell ATMZ into so-calledsubstructure elements SE.

A substructure element SE according to the second ATM adaptation layerAAL2 is composed of a 3-byte-long header SH and a payload area I ofvariable length (0 to 64 bytes). The header SH of a substructure elementSE according to the second ATM adaptation layer AAL2 is in turnsubdivided into an 8-bit-long channel identifier CID, a 6-bit-longlength indicator LI, a 5-bit-long user-to-user indication UUI, and a5-bit-long header error control HEC.

Subdividing an ATM cell ATMZ into substructural elements SE makes itpossible to define a number of channels by means of the channelidentifier CID in an ATM connection, all of which channels are addressedwith the same ATM address consisting of a VPI value and a VCI value.

During a data transmission between the switching system PBX and an ATMhub ATM-HUB, particularly in exchange termination ET and linetermination LT, it is thus possible to define substructural elements SEfor the transmission of channel-oriented data of a subframe CHx.

In addition to the header H of the ATM cell ATMZ, the first byte in thepayload area is defined as pointer Z. This pointer Z points to the firstbyte of a substructural element SE arranged in the payload area of anATM cell ATMZ. This pointer Z can be used for restoring synchronizationbetween transmitter and receiver in the case where one or more ATM cellsATMZ have been lost, such as due to a transmission fault.

In the present embodiment, an individual substructural element SE isdefined for the first payload channel B1, the second payload channel B2,the monitor channel M, and the control channel D, and is thentransmitted in the payload area of the ATM cell ATMZ. By way of example,a payload area I of the substructural element SE with a length of 4bytes is shown in FIG. 4. Following the substructural element SEallocated to the control channel D, the substructural element SEallocated to the first payload channel B1 of the corresponding subframeCHx is transmitted in the payload area of an ATM cell ATMZ.

In the case of an ATM cell ATMZ according to the second ATM adaptationlayer AAL2, in contrast to an ATM cell ATMZ according to the first ATMadaptation layer AAL1, a payload byte is allocated to a channel, to thefirst payload channel B1, to the second payload channel B2, to themonitor channel M and to the control channel D, of a subframe CHx notvia the position of the payload byte in the payload area of the ATM cellATMZ but via the channel identifier CID.

For addressing a communication terminal KE1-KEn connected to an ATM hubATM-HUB, only the VPI/VCI address allocated to the communicationterminal KE1-KEn in the ATM-based communication network ATM-KN is knownin the switching system PBX. Thus, it is not possible, for the reasonsknown in the introduction to the description, to locate the terminalKE1-KEn in the ATM-based communication network ATM-KN, i.e. to associateit with an ATM hub ATM-HUB.

According to the present invention, an unambiguous address is allocatedto each ATM hub ATM-HUB and, if necessary, each ATM network node in theATM-based communication network ATM-KN for locating a communicationterminal KE1-KEn. This address is stored in a non-volatile memory of theATM hub ATM-HUB and can be retrieved on request. If, for example, afault is reported to the switching system PBX, or if it is necessary forany other reason to determine the association of a communicationterminal KE1-KEn with an ATM hub, the switching system PBX transmits acorresponding request message by means of the VPI/VCI address of thecommunication terminal KE1-KEn stored in the switching system PBX.

For such a request message, the bits transmitted in the monitor statuschannels MR, MX are both set to the value 1 (MR=1, MX=1) oralternatively to the value 0 (MR=0, MX=0). Furthermore, it is possibleto establish a special protocol by means of which a message transmittedby the switching system PBX to a communication terminal KE1-KEn isidentified as a request message. This protocol can then be transmittedvia the control information channel D or the monitor channel M from theswitching system PBX to the ATM hub ATM-HUB associated with thecorresponding communication terminal KE1-KEn.

If an ATM hub ATM-HUB receives such a request message (MR=1, MX=1 orMR=0, MX=0), the ATM hub ATM-HUB transmits the address allocated to itin the ATM-based communication network ATM-KN via the monitor channel Maccording to the IOM-2 data format. The switching system PBX canassociate the wanted communication terminal KE1-KEn with an ATM hubATM-HUB by means of the address transmitted via the monitor channel M.

The address of the ATM hub ATM-HUB is advantageously octet-oriented,i.e. the length of the address is a multiple m (m=1, 2, 3, . . . ) ofone byte. This provides for simple transmission of the address via themonitor channel M since the latter has a bandwidth of one byte pertime-division multiplex frame IOMR.

Although modifications and changes may be suggested by those skilled inthe art to which this invention pertains, it is the intention of theinventors to embody within the patent warranted hereon, all changes andmodifications that may reasonably and properly come under the scope oftheir contribution to the art.

1. A method for identifying a hub in a communication network having aplurality of hubs connecting communication terminals to a switchingsystem and using a time-slot-oriented data format formed from a periodicsequence of channel-oriented information segments for data transmissionbetween the communication terminals via the hubs and the switchingsystem, said method comprising: associating each of the hubs with anunambiguous address in the communication network; requesting the addressof a respective hub by the switching system via a request messageaddressed to one of the communication terminals connected to therespective hub; and transmitting by the respective hub the address ofthe respective hub via the communication network to the switching systemin an agreed information segment upon the request.
 2. The method ofclaim 1, wherein the request is made during a message transmission fromthe switching system to the communication terminal.
 3. The method ofclaim 1, wherein the request is made during a message transmission fromthe communication terminal to the switching system.
 4. The method ofclaim 3, wherein the address is transmitted in a monitor channeltransmitting configuration information of the time-slot-oriented dataformat.
 5. The method of claim 4, further comprising the step of:indicating the request by transmitting an agreed bit combination in asignaling channel of the time-slot-oriented data format.
 6. The methodof claim 4, further comprising the step of: indicating the request by asimplified protocol being transmitted in the signaling channel or amonitor channel, which transmits configuration information concerningthe time-slot-oriented data format.
 7. The method of claim 6, whereinthe time-slot-oriented data format is a standardized Integrated ServicesDigital Network Oriented Modular Interface data format.
 8. The method ofclaim 7, further comprising the step of: indicating the request by bitstransmitted via monitor status channels of the Integrated ServicesDigital Network Oriented Modular Interface data format to the hub beingidentical.
 9. The method of claim 8, wherein the address length is oneof, one byte and an integral multiple thereof.
 10. The method of claim9, wherein a data transmission via the communication network takes placeon the basis of the ATM data format.
 11. The method of claim 10, whereina bi-directional conversion is made between the time-slot-oriented dataformat and the ATM data format for transmitting data via thecommunication network by the switching system and the hub.
 12. Themethod of claim 11, wherein the bi-directional conversion between thetime-slot-oriented data format and the ATM data format takes place inaccordance with a first ATM adaptation layer AAL-Type
 1. 13. The methodof claim 12, wherein the bi-directional conversion between thetime-slot-oriented data format and the ATM data format takes place inaccordance with a second ATM adaptation layer AAL-Type 2.